The process of nixtamalization of corn kernels in order to obtain corn dough for the production of tortillas and other articles has long been known. This traditional nixtamalization process comprises admixing one part of whole corn kernels with two parts of an alkaline solution, generally an aqueous 2% by weight lime solution, and then cooking or boiling the mixture, thereafter permitting the cooked product to steep or soak for a period of from 12 to 14 hours, after which the nixtamalized kernels are subjected to a draining operation in order to remove the cooking liquor ("nejayote"). The kernels are then washed with water several times to remove any solubilized products and the excess of lime, and the cooked and nixtamalized kernels (nixtamal) are ground in disk mills, with the addition of small amounts of water, in order to obtain a dough suitable for the manufacture of tortillas. Tortillas are obtained from this dough by forming thin disks of the dough having a diameter of from 12 to 15 cm. and subjecting said disks to a final cooking operation on metal or ceramic plates for periods of about 1 minute divided into 15 seconds, 30 seconds and 15 seconds on alternate sides, at temperatures of from 180.degree. to 200.degree. C. on the surface of the plates.
In view of the ever growing importance of the market for food products derived from tortilla masa dough (nixtamalized corn dough), which is illustrated by the fact that, for instance, during the year 1980, the consumption per capita of tortillas in Mexico was of about 70 kg., various efforts have been made in order to improve the traditional nixtamalization process. All the variations accomplished, however, merely refer to the ratio of water to corn, lime concentration, temperature and time of cooking, washing steps and the like, as illustrated in the following Table 1, but without however affecting in any respect the traditional characteristics of the nixtamalization process described above.
TABLE 1 __________________________________________________________________________ CONDITIONS OF NIXTAMALIZATION Corn Water CaO Temperature Cooking time Steeping time (Parts by Weight) (.degree.C.) (min) (hours) Washings __________________________________________________________________________ 1 2 0.02 80 20-45 14 2-3 Illescas, R. (1943) 1 1.2 0.05 94 50 14 3 Bressani, R. (1958) 1 2 0.02 92 0 12 -- Vaqueiro C. (1969) 1* 2 0.02 87-90 50 0 -- Vaqueiro C. (1969) 1 2 0.01 boiling 0 12-15 2 FAO, 1979.sup.1 1* 2 0.01 76 100 0 2 FAO, 1979 1 3 0.01 boiling 20 15 -- Bazua, C. A. (1979) 1 Supersaturated 70-110 0.6-5 0.5-2 0 U.S. Pat. No. 3,083,103 lime (pressure) 1 3 0.01 -- -- -- -- Bedolla, S. (1982) __________________________________________________________________________ *Accelerated nixtamalization .sup.1 Examination of Processes and Products originated from Corn Flour, 1979 FAO, IMIT.
For instance, in U.S. Pat. No. 3,083,103 to Anderson et al, a process for the obtention of corn masa dough is described, wherein the step of processing the corn kernels is carried out in the presence of a supersaturated solution of calcium hydroxide in water, and by using a steam pressure ranging from about 5 to 25 pounds per square inch during a period of time of from about 40 to 5 minutes. This process obviously accelerates the nixtamalization process considerably, but at the expense of affecting the flavor and other properties of the masa dough, and produces a masa dough which is not suitable for the manufacture of tortillas but which is rather used for the manufacture of crunchy flakes.
In U.S. Pat. No. 4,250,802, a different process is also reported, which includes preheating of the kernels previously treated with a lime water spray to deliver partially cooked grain in a comparatively dry state to a mill for pulverization thereof, following which it is made into a dough which is finally cooled and formed into the desired end product such as tortillas or corn flakes.
As it may be seen from the above, all the prior art processes for the production of corn dough are based on the treatment of the whole corn kernel with an alkaline solution which are mere variations of the traditional process of nixtamalization described above.
It is a well known fact however, that both the masa dough manufactured from nixtamalized corn kernels and the tortillas manufactured therefrom are quite unstable and have a relatively short shelf life, whereby in countries where the consumption of tortilla is relatively high like in Mexico, wherein the consumption per capita is of about 70 kgs per year, a relatively large amount of nixtamal mills and tortilla manufacturing shops must be installed, such that the tortilla manufacturing shops may obtain on a daily basis the masa dough from the nixtamal mills, to manufacture tortillas to be sold on the same day to the final consumers, who in turn prefer to buy tortillas on a daily basis, in order to avoid hardening of the product. For instance, in Mexico there are approximately 25000 nixtamal mills and 23000 tortilla manufacturing shops to satisfy the needs of the Mexican market.
Considering the above, the workers of the prior art led their efforts in two different directions, one of which was to improve the stability of the end products, namely, the tortillas and one other alternative, namely, to produce a dried corn flour which might have a long shelf life and other advantages.
The first alternative is represented by the process of Manuel Jesus Rubio et al, U.S. Pat. No. 3,730,732, which reports that the yield of dough and tortillas is increased by incorporating water soluble alkaline substances in the dough. Also, Rubio et al report that this process of adding soluble alkaline substances to the dough, retards the microbiological spoilage of tortillas which are unleavened, unshortened food products made of nixtamalized corn or nixtamalized corn flour. This type of processes for improving the shelf life of tortillas, do not solve the problem of having a product for the manufacture of tortillas that may be preserved for relatively long times without any spoilage, since the only improvement is in the end product, namely, the tortillas, which nevertheless tend to become hard and brittle, regardless of the fact that they may or may not be affected by microbiological spoiling processes.
Therefore, the most universally accepted technology has been the second above mentioned alternative, namely, the production of corn flour, more particularly of nixtamalized corn flour which may serve as an instant product for the manufacture of tortillas and other corn products, even after being stored for relatively long times without any spoilage. The nixtamalized corn flour presents a number of advantages with respect to the dough produced by the traditional method described above, such as the following ones: (a) the corn flour may be stored at room temperature for relatively long periods of time; (b) the production and distribution may be adjusted to the demand; (c) the product is highly homogeneous; (d) the hygienic conditions during the manufacture of corn flour are much better and are controlled in a strictly regulated manner than those prevailing in the manufacturae of masa dough; (e) if the end products such as tortillas or other corn products such as corn flakes are to be used as carriers for some other nutrients, these nutrients may be easily incorporated in the corn flour.
Numerous slightly different methods for the manufacture of nixtamalized corn flour have been reported in the literature, but the method which has gained more popularity and which is and has been up to the present time the most widely utilized one on an industrial level, is the process of accelerted nixtamalization developed by the Mexican Institute of Technological Research (IMIT) (Instituto Mexicano de Investigaciones Tecnologicas) back in the year of 1951 (U.S. Pat. No. 2,584,893). This process comprises an accelerated nixtamalization of the whole corn kernels for a period of time of from 45 to 60 minutes at a temperature in the vicinity of the boiling point, with a weight ratio of corn to water of 1:2 and a calcium hydroxide concentration of 1% based on the amount of corn. The whole corn kernel nixtamalized by the above process and having a moisture of from 40 to 45% is drained and washed, after which the nixtamalized kernel is subjected to impact milling and is dried for obtaining a dried corn flour.
E. L. Wimmer et al, U.S. Pat. No. 3,404,986, patented Oct. 8, 1968, report a method of manufacturing a corn flour having a rich whole corn flavor as distinguished from the flavour which results from lime treatment, which essentially comprises the control of the moisture content of a previously prepared corn meal for partially gelatinizing the moistened meal between closely adjusted heated rotating rolls to form flakes which are thereafter ground to obtain the corn flour. This process, however, by not using the nixtamalization step, namely, the treatment with an alkaline solution, may be regarded as a process which is inadequate for the preparation of a masa dough for the manufacture of soft and tender tortillas, since the fiber of the hull of the whole corn kernels is preserved without any transformation, which may give rise to an unsuitable plasticity in the masa dough for forming the disks that are called tortillas.
Fausto Celorio, Mexican patent No. 125,285, of Apr. 25, 1972, describes a different process and apparatus for the obtention of nixtamalized corn flour by using a dry process, which essentially comprises admixing a previously prepared corn meal with an appropriate amount of lime and heating the mixture in a chamber in a fluid bed, so as to release moisture from the particles of the corn meal, such that a humid and hot atmosphere is formed within the nixtamalization chamber, sufficient for effecting nixtamalization of the corn meal without the addition of an aqueous medium. This process, however, may be regarded as producing poor results in view of the fact that the admixture of the corn meal and the lime in a powdered state, produces lack of homogeneity in the nixtamalization process, with the consequent difficulties in quality control of the corn flour obtained by said process.
One other process for the obtention of corn flour for the manufacture of tortillas is that proposed by Molina et al, Journal of Food Science, Volume 42, No. 6 (1977), page 1432 et seq, which comprises milling the whole corn kernel and admixing the corn meal thus obtained with a 0.3% lime solution in a weight proportion of 3 to 1. The moist mixture is dried in a drum dryer and the product is thereafter ground for obtaining an instant corn flour for making tortillas. This process, however, does not introduce any advance in the art and, instead, requires a cumbersome drying procedure which is of relatively difficult control. Besides, the nixtamalization of preground material cannot be controlled appropriately.
Bazua et al, Journal of Food Science, Volume 44 (1979), page 940 et seq, describe a process for the manufacture of nixtamalized corn flour which comprises milling the whole corn kernel, adding to the thus obtained corn meal 0.2% by weight of calcium hydroxide and subjecting the product to extrusion with the addition of water. The product resulting from this operation is a moist flour which is subjected to drying and grinding for the obtention of an instant flour for making tortillas.
As it may be seen from the above, all of the processes either for obtaining masa dough or for obtaining instant flour for making tortillas and the like, have resource to nixtamalization of the whole corn kernel, and particularly introduce the concept of an accelerated nixtamalization treatment, which produces a plurality of physical and chemical changes that bring as a consequence loss of solids and changes in the constituents inherent to the corn kernel. It has been reported that the loss of solids reaches values of from 5 to 14%, mainly caused by solubilization due to the thermal treatment in an alkaline liquour. The components which are lost with more frequency are, the 33 to 40% of the fats present in the germ, the 32 to 46% of the raw fiber of the hull, and the 10% of the nitrogen of the proteins contained by the corn kernel.
At the same time, the nutrient value of the corn is affected, mainly due to the insolubilization of certain proteins, the release of certain amino acids and the modification of the leucine/isoleucine ratio and the increase in the availability of niacin.
The changes produced in the hemicellulose are connected with the hydrolysis and solubilization, which releases highly hydrated cellulose fibriles having a high effect in the rheologic and mechanical characteristics of the dough and the tortillas. These changes are more drastic in the traditional nixtamalization than in the accelerated nixtamalization treatment, and the type of grinding which is used in both processes exerts a different effect on the hull, inasmuch as in the instance of the traditional nixtamalization described above, the grinding by attrition with stone disks forms fibriles, while in the accelerated process the grinding is an impact grinding and a shear grinding, which generates the formation of fibers joined in an irregular staple form, and has a marked effect on the characteristics of the dough and the tortillas in what refers to parameters such as penetration, elasticity, plasticity, resistance to bending, and the like.
In connection with the proteins, these suffer an initial solubilization process which permits migration thereof towards the cooking liquor, although thereafter said proteins are insolubilized by the action of the temperature within the cells. This phenomenom is extant both in the traditional nixtamalization and in the accelerated nixtamalization.
The starch, on the other hand, in the instance of the traditional nixtamalization, is merely homogeneously hydrated permitting the release of the starch granules during grinding, whereby said starch is obtained in a very fine type of particles and, at the same time, in view of the type of thermal treatment and grinding under humid conditions, no damage through gelatinization or through mechanical action is produced. In the instance of the accelerated nixtamalization, the peripheral zone of the endosperm presents gelatinization of the starch and, while this might permit an increase in the absorption of water during preparation of the dough, it also facilitates the evaporation of water during cooking of tortillas, whereby the mechanical properties of said products are detereously affected. It is to be noted that during the cooking of the tortilla a total gelatinization of the starch granules is produced.